Humans have a knack for remembering faces. And when someone forgets yours, it tends to sting.
The same is true, it turns out, for the Northern paper wasp (Polistes fuscatus). Though often maligned as painful pests, wasps have more in common with humans than some of us might like to believe—including a particular aptitude for recognizing individuals by their facial features.
While scientists have been aware of this phenomenon for years, what’s less clear is how these wasps accomplish this feat: The ability to distinguish faces could be inherited, or something learned through experience. Now, in a new study published in the journal Animal Behaviour, researchers report that part of the process is built into the wasp brain—and species lacking this innate ability may never entirely make up for the difference.
“This work is absolutely groundbreaking,” says Adrian Dyer, who studies the science of vision at RMIT University in Australia but was not involved in the research. “It shows a bridge between expertise… and a more hardwired system.”
Even among paper wasps, P. fuscatus is exceptional: This species seems uniquely equipped to home in on facial features—and it might have something to do with their social structure. Many P. fuscatus wasp colonies are founded by multiple females who tussle for dominance. Once a pecking order is established, each queen can take on a unique social role, which goes on to dictate how workers integrate into the nest hierarchy. As such, the ability to recognize individuals is essential for these wasps to maintain stable relationships within the colony, affecting everything from displays of aggression to division of labor and food allocation. Accordingly, the facial features of P. fuscatus wasps are highly variable.
In a closely related species, Polistes metricus, or the metricus paper wasp, nests more commonly support single-queen monarchies—a simplified hierarchy that eliminates the need for detailed distinctions between wasps. Unsurprisingly, metricus faces are mostly indistinguishable, even to their own kind.
Study author Elizabeth Tibbetts, an evolutionary biologist at the University of Michigan, realized these P. metricus’ shortcomings might just be the key to unraveling the cognitive basis of facial recognition. Face-savvy P. fuscatus individuals are reared in the presence of facial diversity—which means they’re acquainted with an assortment of colors, shapes, and sizes right from the get-go, whereas metricus wasps don’t enjoy the same privilege. It’s a classic nature versus nurture question: Are P. metricus wasps are inherently ill-suited to the task, or are they simply deprived of the necessary education?
To test the influence of experience on face learning, Tibbetts and her colleagues set up a series of hybrid hives. In some, P. fuscatus and P. metricus wasps were reared with their own kind; in others, they were mixed with each other. The researchers also added a third, more distantly-related species, Polistes dominula, or the European paper wasp, to the mix. P. dominula individuals take note of features that indicate physical prowess—the faces of stronger wasps have a more splotchy pattern of black spots—but these motifs are too broad to identify individuals. Tibbetts compares the system to belt colors in a karate studio. “To tell how tough someone is, you can look at their belt color,” she explains. “But you don’t need to memorize individual faces.”
After five days of co-mingling, the researchers enrolled the wasps in a face-learning boot camp. The wasps were trained to make their way through a convoluted portrait gallery of different P. fuscatus faces—a perfectly pleasant setup, save for the fact that the floors of the museum-like maze were electrified. Some of the images, however, were placed in safe, no-shock zones. The researchers tracked whether the wasps were able to use these images to navigate themselves to safety, even when the photos switched locations—a sign that they recognized and remembered these faces’ distinctive features.
As expected, P. fuscatus that had pow-wowed with their own species came out ahead in this face-off, quickly learning to discriminate between safe and unsafe images. The same wasn’t true, however, for P. metricus and P. dominula housed with their own kind. This made sense: Only the fuscatus wasps were gleaning instructive information from their peers, and putting it to good use. But Tibbetts and her colleagues found that P. fuscatus also seemed to hold its own when it bunked with P. metricus wasps. Even without direct exposure, P. fuscatus showed a flair for faces—indicating that the P. fuscatus brain might have some unique, face-discriminating hardwiring.
But this wasn’t the entire story. Tibbetts was next shocked to see that P. metricus wasps—which normally can’t tell faces apart—were also able to successfully maneuver their way through the face maze if they had first fraternized with P. fuscatus wasps. The metricus wasps never did as well as true P. fuscatus wasps, but they outperformed their unexposed peers. Though the metricus wasps had spent only five days with P. fuscatus, this brief stint had apparently been enough for them to learn some of the tricks of the trade. “I thought experience would matter,” Tibbetts explains, “but I didn’t think they would really get better.”
When the researchers repeated the experiment with photos of P. fuscatus lacking antennae—a modification that jumbles the ability of these wasps to recognize a face as a face—neither wasp species did as well. This reinforced the idea that face specialization wasn’t just about recognizing general patterns, like karate belt colors; rather, there was something special about the face itself.
“This contributes to a growing literature on the idea that things aren’t black and white: It’s not just nature or nurture,” says Amy Toth, an entomologist at Iowa State University who did not contribute to the new finding. “It’s the interaction that leads to the development of this complex behavior.”
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Sadly, P. dominula was not so lucky. Regardless of the company it kept, these wasps didn’t show any particular proficiency for distinguishing faces. For them, experience alone wasn’t enough, indicating that inheritance still plays a big role in face specialization.
It’s still not entirely clear what underlies these differences between species, but Tibbetts theorizes that there may be an ancestral influence. P. fuscatus and P. metricus are much more closely related than either species is to P. dominula—and P. metricus’ latent abilities may be a holdover from its past. But until far more wasp species are studied, no conclusions can be definitively drawn, says Seirian Sumner, who studies wasps and other social insects at University College London in the United Kingdom but did not contribute to the new research.
Even more far-flung is the evolutionary distance between humans and wasps. But the fact that the two species have managed to converge on a similar skill fascinates Tibbetts. “Often, when I’m studying wasps, I can’t believe how smart they are,” she says. “They can do so many complicated things. But at the same time, maybe if wasps can do it, maybe you don’t have to be that smart to do these things.”
That’s not to knock on wasps, which certainly suffer from an image problem in the eyes of humans, perhaps unjustly so. Dyer, the vision scientist, thinks studies like these are deeply informative—not just for our understanding of evolution, but also for unexpected applications like machine learning. Insect brains have far less computational power than the human mind, but can still perform exceptionally complex tasks, Dyer explains. “There must be some efficient ways in which miniature brains can do this,” he says. “We can derive real tricks from simple biological systems.”
Tibbetts is also intrigued by this line of questioning. Next, she hopes to uncover what’s actually happening inside the wasp brain during these complicated learning tasks—and if there are further parallels between humans and these ingenious insects.
“This work really demonstrates why we should love wasps,” Toth says. “They’re fascinating creatures with complex social behavior. They may be the closest thing you can find to a human in an insect.”
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